Dormant viruses that most people carry for life without symptoms reactivated in nearly half of patients hospitalized with COVID-19, and that reactivation tracked with how sick those patients became, according to a large observational study published this week in Nature.
The finding does not mean COVID-19 causes new infections from outside the body. It means that viruses already living quietly inside patients, kept in check by a functioning immune system, started replicating again during severe illness. Most people carry roughly eight to 12 generally harmless viruses at any given time, and physiological stress can wake them.
